This invention relates to a land vehicle suspension control system.
By "land vehicle" is meant a vehicle adapted for motion over the land in contact therewith, examples being motor cars, motor cycles, tractors and tracked vehicles.
In particular, the invention relates to a land vehicle suspension control system for a land vehicle having an active suspension system.
An active suspension system is a suspension system in which conventional suspension components, such as springs and dampers, are assisted or replaced by actuators operable, for example in response to command signals from a microprocessor, to correct, change or control the attitude of the vehicle. An aim of such active suspension systems is to minimize variations in the forces experienced by the vehicle body, thereby improving vehicle safety and enhancing driver and passenger comfort.
The command signals which control the actuators are generally derived from measured values of a number of variables defining the vehicle's attitude. In a truly active suspension system, there is the capability of controlling the actuators to respond to measured road inputs, that is due to perturbations in the road surface, while the actuators can be controlled not to extend and contract in response to loads imposed on the vehicle suspension by virtue of vehicle acceleration and cornering and loads carried in the vehicle.
Active suspension systems are well known. For example, EP-A-0114757 discloses an active suspension system for a four wheeled motor vehicle in which force measurements are taken at the points of support of the vehicle body on each wheel/hub assembly and processed to produce a demanded output of the actuator secured to operate between the respective wheel/hub assembly and the vehicle body.
The attitude of the vehicle can then be controlled by converting the forces measured at the points of support to a set of modal forces (e.g. heave, pitch, roll and warp forces), from which the actuator outputs required to overcome the combined modal forces in order to maintain the desired attitude of the vehicle are then calculated.
A significant advantage of such an active suspension system is that the suspension characteristics of the vehicle can be continuously altered to accommodate varying road conditions and/or operating conditions of the vehicle. This facility permits the construction of a vehicle which has improved safety characteristics, since it is possible to maintain a greater degree of contact of the vehicle wheels with the land, and the behaviour of the vehicle is likely to be more predictable to the driver, than in the case of a vehicle not having an active suspension system.
Known active suspension systems include means for manipulating the values of the modal forces to produce a demanded output of actuator means arranged to oppose the modal forces, thereby maintaining a constant force on the vehicle body.
However, previous control systems used in conjunction with active suspension systems have operated on the principle of producing a demanded position of the actuator means and operating the actuator means accordingly. The actuator means generally includes a hydraulic actuator operating between each wheel/hub assembly and the body the of vehicle.
The frequency response of an electro-hydraulic actuator can be improved dramatically if the control processor can be arranged to output a velocity, rather than displacement demand. When this is the case the primary input to the actuator is a velocity demand.